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Why is the APU located in the tail for almost all commercial aircraft?
I know there are planes whose APU (Auxiliary Power Unit) is located elsewhere, but for the most common commercial jet aircraft (A320, B737, B747, A330,...), the APU is located in the tail.
Is there a good reason for that (place, weight, airflow,...)?

The B727 has the APU in the main landing gear wheel well, this is in the middle of the aircraft, between the wings.
The APU EXHAUST is on the right top inboard side of the wing.

Dead space... Not much room in the tail to put other stuff, and it fits. Plus it has a nice empty space just outside for the exhaust pipe to exit without the hot gasses hitting anything.

Put the APU in the nose and you need a long pipe somewhere to get rid of the exhaust. More weight, more space, etc.
Put it in the wing and you're looking at uneven weight distribution (you want it at or near the centerline).
Leaves the tail area as a logical place, and there just happens to be space there as well in most aircraft.

and most pressurized aircraft have most of the tail section as unpressurized so you don't have to compromise the structural strength to allow the APU to reside there (it make no sense for it to be in he pressurized section)

@ratchetfreak true, but there's other places like the wing root that might work as well for that.

but that is where the PACKs are

@ratchetfreak and on many the landing gear. Hence the dead space answer... Of course the PACKs could have been located in the tail and the APU in the wing root, if it made more sense to do that.

For anyone else wondering: PACK = Pneumatic Air Conditioning Kit or sometimes PACS = Pneumatic Air Conditioning System

I guess wing root has a lots of fuel in it. Hot engine and flammable doesn't go well together.

@vasin1987 you may be be surprised to learn that that fuel is used as a heatsink for the airco units...

There are a few reasons that the APU is located in the tail in most modern aircraft.
As previously mentioned, the space in the tail is otherwise mostly unused. Aside from hydraulics and such for the control surfaces, there isn't much use for the space. Most aircraft don't have any other spaces like that. Alternate locations like the wing root are generally used for fuel tanks, landing gear, air conditioning packs, and other systems. This area is also outside the pressure vessel, which reduces the number of ducts and such that need to pass through the pressure vessel wall.
Another important benefit is fire protection. Having the APU in the tail places it as far away from the cabin and fuel tanks as possible, and being outside the pressure vessel makes it easier to isolate from those areas.
Having the exhaust exit the tail prevents it from interfering with any other parts of the airplane.
Not having it next to anything else also makes it easier to access for maintenance, generally through doors on the underside of the tail.
The drawbacks of having the APU in the tail include the need to run bleed ducts, fuel lines, and power supply wiring all the way back there. Also, the hydraulics and controls in the tail must be protected in case of a problem with the APU.

"Another important benefit is fire protection. Having the APU in the tail places it as far away from the cabin and fuel tanks as possible, and being outside the pressure vessel makes it easier to isolate from those areas."  Unfortunately, not all of an airplane's essential systems are forwards of the tail...


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How does a flying wing keep from going into a flat spin when maneuvering?
How do flying wings, like the B-2 Stealth bomber, actually keep themselves from yawing out of control without a vertical stabilizer?
For the record, I assume this has to be a simple mechanics process.  Why?  Well flying wings go all the way back to the 30s.  One of the earliest (and my personal favorite) is the N-9M, which was a scale model of the XB-35, a prototype bomber for the allies during WWII.
They didn't have flight control computers back then, and the only control complaints I recall them having is that early versions had a tendency to flip over backwards when approaching stall speeds, well, that and the ground effects were pretty strong. But, no mentions of going into flat spins when going into hard maneuvers (that I recall).
So how do they control that Y axis on flying wings?  Are they perhaps more susceptible to a flat spin than a regular design (even if those risks can be kept to an acceptable minimum)?

With difficulty.

Theres two different approaches, passive and active stability on all three axis.
X axis (roll):
In the X axis, flying wings are stabilized the same as any other plane.
Passive stability is achieved through a slight upwards dihedral between left and right wing.
Active stability is achieved through ailerons near the wing tips which create a controlled differential lift allowing the pilot or flight computer to control the roll velocity.
Y axis (pitch)
Passive stability in the Y axis in traditional planes is achieved through the high-leverage corrective force of the horizontal stabilizer (with the exception of canard type planes where the main wing itself takes this role)
Active stability is achieved through elevator controls on this stabilizer, which increase or decrease the vertical force in one or the other direction.
In a flying wing this stabilizer is not present. Instead the rearward area of the main wing takes this role. For this to work, a stable flying wing needs to have wings that are significantly swept backwards in such a way that the overall torque force at both positive and negative high angle of attack is always decreasing this angle of attack.
Active stability is achieved through control surfaces at the very back of the wing. These are often the same control surfaces also used for Roll control, but deflecting in unison instead of opposite directions (Elevons)
Z Axis (yaw)
Similar to pitch, the passive and active yaw control on conventional planes is done with a stabilizer fin with a rudder at the tail.
In true flying wings this is not present (Some don't even have winglets) But the high wing sweep (usually the wings of a  flying wings meet at roughly 90° angle at the tip) causes a higher drag force at the forward facing wing if the craft yaws to one side, which enacts the required corrective force.
Active control is achieved by causing additional drag through some sort of braking flaps near the wing tips (the actual implementations vary - split elevons - separate break flaps - ...) This can also be augmented by using differential thrust.
(Note: The corrective force is much lower than that caused by a tail fin. As such a powered flying wing should have its engines relatively close to the center, otherwise a one-engine-out scenario would cause an uncorrectable yawing moment. This however limits the effectiveness of differential thrust if the craft is supposed to stay flyable in such a condition)
Speed and stall stability:
A speed stable plane has its nose pitch up at higher speeds and pitch down if the craft gets slower, thanks to the center of gravity being in front of the center of lift, which causes the nose to drop. This is balanced out by a (usually parasitic) downward force from the horizontal stabilizer acting at the tail of the plane. This arrangement of forces should also cause the nose to drop and the angle of attack to reduce in a stall situation.
As a flying wing does not have this stabilizer, a similar balance of forces needs to be achieved through a careful design of wing profile and twist.
If you look at Horton flying wing glider designs for example, they have a "thick" profile creating the majority of lift in the center (which thanks to the wing sweep is also the front)  Towards the end and back of the wings, the profile becomes thinner and more symmetric. At the same time, the wings are slightly twisted, so the intrinsic angle of attack is a few degree lower at the tip (and as such at the rear of the wing) than near the nose.
At high speeds, the front of the wing creates more lift than the back and rises the nose. This part has the highest wing load and will stall first, while the swept back outer wing area - thanks to its profile, lower AoA and lower load will not have stalled yet. The nose drops, and the control surfaces in this rearward part stay functional.
It should be noted that not all flying wing designs did achieve a safe stall behavior. Some, like early 1940's and 1950's American designs failed to implement stall stability correctly, while others (like the B2 bomber) the plane was deliberately designed aerodynamically unsafe to faciliate other features (stealth) which would have been compromised by a "twisted" wing.

Are there any flying wings, past or present, that implement this twist wing design?  Can you add a picture or illustration to show what that looks like (bonus points if it shows how the center of lift is moved viz a vi airspeed)?  Fascinating stuff...

the "lower" wing creates slightly more lift in upwards direction and allows the plane to roll back to horizontal flight - can we please unlearn this nonsense? This has often been claimed and never been true. Dihedral will not right up an airplane.

The author of this answer doesn't seem to be active on this site any more, so I've taken the liberty of removing the sentence Peter pointed out.

Sweepback helps a lot, and the rest is achieved with drag devices near the wingtips.

(Source: aerospaceweb.org)
Did you notice that the B-2 has split ailerons, and they are partially opened during flight? Their drag pulls the wingtip back, and in combination with sweep the forward wing in yaw will have a longer lever arm, so the same drag produces a bigger stabilizing yawing moment.
Differential thrust is not available on gliders, and there are lots of flying wing gliders. Horten III and IV, Fauvel AV-36 and the SB-13 are some examples. The Hortens used speed brakes near the wingtips, and the SB-13 has rudders with differential deflection (70° outwards, 20° inwards) on its winglets to increase the yawing moment.
Directional control is no problem with flying wings, even though directional stability becomes weak at high speed when induced drag is low. Flutter and a low $c_{L max}$ are the real drawbacks. Ground handling, landing characteristics and payload space are others, but can be overcome somewhat.
And flat spins are not possible with flying wings. Their spin modes are all fairly steep due to the lack of a strong inertial moment from the lengthwise distribution of masses.

Fantastic, I've been hoping someobody would swoop in and answer this one!  Can you expand a bit on flutter and CLmax (not sure what that is)?  Or should I just ask a separate question for that?

Sure: $c{_L max}$ is the maximum coefficient of lift. A flying wing needs an airfoil with a low pitching moment, and those create less lift with the same wing area than regular airfoils. A low pitching moment is achieved with reduced or even negative camber in the rear part of the airfoil (google "reflex airfoil" for more info and pictures). Flutter is an interaction of aerodynamic and elastic oscillations which looks from the outside as if the aircraft flaps its wings. It scares the heck out of the pilot, because most flutter ends in the wings (or whatever else which is involved) breaking off

Re "And flat spins are not possible with flying wings." -- I've seen some extremely flat spins in hang gliders.  Pilot's weight shifted quite far toward outboard wingtip.  Spent some time looking for videos on line but haven't found any yet.

@quietflyer This sounds like the flight mode of a maple seed. When the cg is near one wingtip the wing will behave like a one-bladed rotor which is not really a spin. But that is not true for a well balanced flying wing.

Interesting thought-- but even when the pilot is shifted full to one corner of the control bar, that's only a distance of 3 feet or so off center, which is fairly small compared to the wing span of the glider.  Still, interesting thought.

@quietflyer So I misunderstood "Pilot's weight shifted quite far toward outboard wingtip". Still, the imbalance should have a strong effect.

Flying wings use differential thrust for yaw control instead of vertical stabilizers and rudders. Some also have small outboard rudders or spoilers for this purpose.

Jet engines have very slow response to thrust setting. So you can use differential thrust for gentle turn, but there's no way you to recover stall, or even damp dutch roll with it.

The B-2 uses differential thrust in stealth mode, and also uses outboard spoilers or "decelerons" when not in stealth mode.

The first aeroplane to be certified inherently stable, the Dunne D.5 of 1910, had a tailless swept wing. A series of biplanes and monoplanes followed, all tailless swept types and some arguably flying wings with bits dangling off.
The key feature which made them stable in pitch was twisting down or washing-out the wing from root to tip, later described as "putting the tail at the end of the wing". (Some tailless types have used special airfoils with a stable centre of pressure, so that the usual destabilising movement with angle of attack is avoided.)
These planes were the culmination of a decade-long search for a plane which was not only stable but could right itself automatically from any position into which it was thrown. His friend HG Wells and licensee Starling Burgess (of the Burgess-Dunne line) both record his habit of jumping up onto a convenient platform and launching small paper models to illustrate the point (Many of these models survive in the Science Museum's archive collection).
To avoid stalling and spinning, the tail was joined to the wing and the incidence variation smoothed out along their common span so that there could be no sudden breakaway on one surface, rather it would begin at the root and the nose would then drop to restore smooth flow. The tips were arranged to give proverse yaw, so that banking into a turn would apply the correct amount of yaw for a smoothly coordinated turn. Part of this was imbued by actual downforce at the tips (recently incorporated in the Prandtl wing by NASA). The biplanes did indeed live up to his claims and one was flown safely across the Channel through a storm in 1913, conditions in which more than one conventional plane of the day vanished without trace. The monoplanes were slightly different, but their only vice was to stall totally and suddenly when flown too slowly, and "pancake" down gently in a superstall, much like a parachute (even they might have recovered eventually, but he never tried it at altitude).
Jack Northrop, who later pioneered the flying wing in the US, was a big fan of Dunne.

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How does wing sweep increase aircraft stability?
I was told at one point that the sweep of a wing can help with the straight line stability of the craft, in fact I think it's one of the main systems that keeps flying wings flying straight (like the B-2 or N9-M, which comes from the 40s, way before the use of flight computers for stability...).
Why is that?  Are there trade offs between that stability and say, speed?  Is there a such thing as too much sweep?

Directional stability
When a swept wing is flying in a sideslip, the windward side behaves like a wing with less effective sweep $\varphi_{eff}$ and the leeward side like one with more effective sweep. Wing sweep  causes a flattening of the lift curve slope for two reasons:

The effective angle of attack is reduced by the cosine of the sweep angle.
Only the component of speed normal to the quarter-chord line of the wing is creating lift, so a swept wing creates less lift per area than a straight wing.

The increased lift rolls the aircraft, but also produces increased lift-induced drag which pulls it back to straight flight. The sketch above shows this for the flying wing glider SB-13. This effect is so strong that swept, high-wing configurations need anhedral to keep the sideslip-induced rolling moment down.
For completeness, also the side force $Y$ of fuselage and winglets is added and shows that the winglets help a lot to create directional stability. This is needed in case of the SB-13 because it has a nearly elliptical lift distribution. Using a triangular distribution (N9-M) or even a bell-shaped distribution (Horten flying wings) avoids the need for winglets, but causes higher induced drag in straight flight. Another downside is a low directional stability at high speed, because this sweep effect increases with the lift coefficient on the outer wing.
Longitudinal stability
Wing sweep also helps in longitudinal stability by stretching out the wing lengthwise. This is important for flying wings which lack a separate tail surface. By changing flap angles at the center or the wing tips, the lift at the most forward or most backward sections can be changed for pitch control, and more sweep increases the lever arm of these changes. Also, in swept flying wings natural static stability can be achieved without the use of reflex airfoils, but by applying washout. Again, the higher the sweep angle, the less washout is required.
Too much sweep?
Easily! Sweeping a wing creates lots of problems:

Sweep reduces the lift curve slope and the maximum lift of a wing. The maximum landing attitude with a highly swept, slender wing is severely limited by wing tip clearance, so swept wings need powerful high-lift devices.
Sweep causes the boundary layer to be washed outboard, which will cause nasty stall behavior once a specific ratio of wing aspect ratio and sweep has been exceeded. This can be somewhat limited by wing fences, but should better be avoided altogether.
Sweep changes mean that bending moments will partially get converted to torsion moments, requiring a torsional stiffening of the wing.
For flying wings, sweep will let the aircraft center pitch up and down when the wing flexes. This creates a powerful interaction between the fast period mode (which is only moderately damped in flying wings) with the wing bending mode, resulting in flutter.

Why sweep a wing at all?
Generally, an aircraft designer will allow only as much sweep as necessary.
Wing sweep reduces drag when the aircraft flies with transonic or supersonic speed. Now the Mach effects depend only on the normal speed component, so they are proportional to the cosine of the sweep angle. For the N9-M this was not a factor, however, the B-2 benefits from it with a higher drag divergence Mach number.

Can you explain the problem 4 of sweeping the wings? I did not really understand it. I did not understand the words fast period mode and wing bending mode(what do they mean?). I am sorry if I should know what they mean.

@Crafterguy: Yes, but not in the comments. This is an interaction between two eigenmodes, one the short period mode and the other the elastic bending mode of the wing.

@ Peter Kampf: So what downwash angle did you use for the wing tips and what % semi-span does that start at, eg 25% from tips?

@Fred: I gutes you ask about the washout angle. Complicated. We combined washout with flap twist, so there is a 0.8 degree incidence decrease when the airfoil transitions from the HQ34 to the HQ36 at about 50% of span and then a linear -2° washout to the tip, IIRC. This is complemented by 10° of flap twist (I write this from memory, so could be wrong). Since there are two elevons per wing, the outer ones with 3 times the throw of the inner ones, details depend on the flap position which has to match the cg location.

@ Peter: Thank you. For all the non-aerospace engineers, IIRC stands for centre of pressure, HQ34 was the airfoil used?

@Peter: Were the mating ends of the transition between HQ34 and HQ36 a blended airfoil? i.e wing sections were: HQ34 to HQ34/36blended, and HQ36 to HQ34/36blended

@Fred: IIRC = if I recall correctly. HQ34 is the inner airfoil, HQ36 is the flap airfoil. Blending was done over 30 cm of span just inboard of the elevons.

@ Peter: I assume you have a main spar at 25% x/c, and a rear spar for your elevons at 75% x/c, but what about your spoiler? It seems to be at about 50%, which would need it's  own "spar" between 2 ribs. Is this correct?

@Fred: No, the spar ran from more than 40% of chord at the root to 12% at the tip for aeroelastic tailoring. The elevons are 19% of chord. Spoiler is right behind the spar at a place where its effect doesn't change pitch.

A big benefit of swept wings is lower drag at high speed. When an aircraft with swept wings yaws, it is effectively increasing the sweep of the wing in the direction of the yaw, and decreasing the sweep of the other wing. So the wing opposite the direction of yaw will have less sweep, therefore more drag, counteracting the yaw. Likewise, the other wing will have higher sweep and less drag.
Of course you can have too much sweep, otherwise all planes would just sweep their wings completely away and look like the X-24. Your previous question addresses other properties of swept wings well:
Why do some military aircraft use variable-sweep wings?
There are certainly tradeoffs, but vertical surface area is still a more effective means of providing stability. The effect on swept wings of 1 degree of yaw will be less than the force created from the rear fuselage (and vertical stabilizer) being at effectively 1 degree angle of attack. Of course flying wings will primarily rely on this differential drag for stability, but they use things like clamshell brakes to create the necessary drag for extra stability and control.
More sweep is better for speed, but not so good if you want to go slower. So sweep is going to limit low speed performance, and the stability improvement will also be less as airspeed decreases.

As for flying wings, longitudinal control (let alone stability) depends on being able to being able to move the center of lift backwards and forwards. That would be hard to do with a straight flying wing which doesn't have a separate tailplane or carnard -- all the lift is generated at the same (longitudinal) position.
On the other hand, if your flying wing has sweep, you can get longitudinal control by putting control surfaces at different distances from the center of the aircraft. Increasing lift at the outer parts of the wing will produce a nose-down moment, and vice versa.

A straight flying wing can be longitudinally controlled with training edge flaps. They re-distribute the lift distribution chordwise. See the Fauvel flying wings for example.

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Can an airline lay off its flight attendants and use pilots to fill the role?
IcelandAir recently announced that it will be laying off its entire flight attendant staff, and plans to have pilots fill the role in the meantime.
Can an airline lay off its flight attendants and replace with pilots without requiring further training or certification? Generally, pilots are trained to fly the airplane and oversee the safety of the flight - but are they qualified to act as flight attendants? Is there any area a flight attendant maybe more qualified than a pilot, excluding passenger service and a smile on the face?

I think most pilots wouldn't work as flight attendants regardless of airline's wishes.

@GdD If I understand the linked article correctly, the pilots will still be working as pilots on some flights, but as flight attendants on other flights because they currently have more pilots than they need. If your options are doing that or quit / being fired in the current situation, I guess most pilots would do it and be happy they still have a job.

I agree to your understanding. I read it as two pilots are in front and other off duty pilot (maybe four for a 737) work as flight attendants.

I think there are requirements to be flight attendant that pilots don't meet (because it is not their job). I'm thinking of handling hardly-controllable passengers (whatever the cause (medical, alcohol, hooligan,...)), everything related to first aid in flight (remember that historically flight attendant were nurses), and I may miss lots of aspects (I'm not a steward, I don't know much about this job).

As an aside, "firing" an employee is generally for cause, i.e. they did something wrong, and it carries a negative connotation.

@MichaelHall "firing", "furlough", "laid off", "reduction in force"... doesn't matter what you call it, people still end up without income. Sure, they may get some severance pay, but it won't last forever.

On the bright side, if this happens, there won't be any panicked announcements in the cabin, "Does anyone here have any flight experience?" ;)

@FreeMan, true enough, but lay off is still a better term than fire in this context.

The solution to the dual problem of soothing the bruised egos of pilots converted to flight attendants, and the issue of their possible lack of experience in getting cooperation out of unruly passengers, is to arm these people with really big guns, openly carried.  And cowboy hats.  And cattle prods.

And the risk of permanently annoying the flight attendants who would also prefer to continue with paid employment.

When I was flight crew on CRJs for a private operator we got abbreviated FA training for pilots, which was mostly a kind of crowd control course, taught by a contract FA. Their training is about managing a chaotic cabin full or panicking passengers. FA's are more or less under-cover riot control cops who spend their careers working as servers/attendants and are very unlikely to use their actual training.
So theoretically, airlines could offer flight crews FA postions, if they were willing to take the pay cut and were willing to be reminded every day where they are not, performing that undercover waiter/waitress function.  Yes, additional training would be required because airline flight crews don't get significant FA (crowd control) training and a pilot would have to take the FA course.
This is an opinion, but I would say not a difficult call; you would NOT get any takers. Every pilot will take the furlough and go look for another flying job, or change careers.  There is just no way that someone who loves flying enough to jump through all the hoops to get into a flight deck would take that kind of "demotion" (maybe... maybe... one person here or there would agree to it out of sheer desperation, but not enough to be significant).

I know several pilots who started their airline career from being FA (often while working on their license or flying as GA instructors). Being in the airline still raises your prospects of getting the flying job.

That can work but you will never see them going the other direction tho.  Huge step down.

At least some of the remarks here show a very poor understanding of what cabin crew are and what they do.
No, pilots cannot replace cabin crew without substantial formal training.
Cabin crew are highly trained professionals, just like pilots. It's true that unlike pilots they are not in command of the machinery, and that their role requires them to do many much less glamorous, high-prestige tasks than pilots have to do.
That doesn't make them any less professional or trained. Instead, they manage people in large numbers and their behaviour and look after their needs, in an environment that is both unnatural and stressful, and tends to provoke poor behaviour.
Amongst other things, they typically speak multiple languages, have first-aid skills and can deal equally effectively with a weeping widower, a gang of drunken oil-rig workers returning, someone having a panic attack, an over-entitled business executive, etc etc etc.
In cases of emergency, they are responsible for ensuring the safety of dozens or hundreds of frightened people, by getting them to stay calm and  follow instructions.
Anyone who imagines that the people with these skills and training could effectively be replaced with people lacking them is dreaming.

@Daniela Procida, I agree 100 percent with your answer, but I disagree that a pilot would for some reason be unable to attain the skills needed as some have implied in comments on my answer. Most pilots are just as capable of completing the "substantial formal training" you allude to as any random applicant off the street. Agree or disagree?

Of course there's no intrinsic reason that pilots wouldn't be able to attain the skills... but they'd need to attain them through formal training and they wouldn't automatically have them.

Thank you.  I never said they wouldn't need any cross training, yet still some took exception with my answer.  I may add some rationale behind my position...

Most pilots are not currently qualified to serve as flight attendants, but they could be trained easily enough following an abbreviated syllabus.
Since pilots are already familiar with all the aircraft emergency equipment and procedures, training would just need to focus on specific tasks in different areas of the cabin.  That, plus operation of beverage and food service equipment.
It wouldn't be a difficult transition if the pilots were willing.

yes requirement are less in the sense it takes less time to form a flight attendant, but requirements are quite different. Pilots are more into technical stuff while flight attendant are more into handling humans. As an extreme case, if you are unable to understand a panicking passenger, it is OK to be a pilot (1st priority: fly the plane, even if it involves locking yourself alone in the cockpit) but not to be a steward.

@Manu H, are you saying you think that a dual qualified pilot/flight attendant would be less capable of handling a panicking passenger than a person who was qualified only as a flight attendant because they would be hampered by their technical pilot knowledge? Because I heartily disagree.

I think I'd disagree about the training being easy.  Being a good pilot  requires much different personality traits than being a good flight attendant (just as being a good engineer requires different traits than being a good manager), and those traits are not really something that can be trained.

I didn’t say the training itself was necessarily easy, but by the time you are an ATP you have proven yourself very capable of being trained.  And while I agree that personality traits cannot be trained in, appropriate behaviors certainly can be.  And again, by the time you are an ATP and have made it through the screening process to be hired by an airline large enough to use flight attendants you have obviously demonstrated some basic people skills...

@MichaelHall I'm saying it is not the same job and being able to think like a pilot does not make you able to be a flight attendant (and the other way around). As a flight attendant you must deal with passenger that doesn't have formation or knowledge, and you have to communicate with them even if they hardly speak your language and in emergency situation. Not the same as a pilot whose formation include aeronautic english. Definitely not the same job, not the same primary concerns, not the same way to communicate,...

@Manu H, all easily overcome by training and experience.  Flight attendants have to start somewhere too, my point is that pilots have a head start in a lot of areas.

@Michael Hall: NOT easy, judging by my experience with similar job shifts.

@MichaelHall I disagree. Some people are best at dealing with human relationship (and are more fitted to be cabin crew) and other with technical relationship (and are better fitted to be pilot). Following your mind, anyone (even those passing out seeing blood) can make any job (even doctor). My point is a pilot is not necessarily fitted to be a cabin crew, whatever the training.

@Manu H, you seem to presume that people skills and pilot skills are mutually exclusive.  They aren't.   Maybe for some, but definitely not for all.

It could work both ways.  Having a steward that is qualified to fly or "sit in" as a flight engineer in high workload situations (take off/landing/illness to pilot or copilot/inclement weather/aircraft malfuction) would be an asset, especially on a smaller carrier.  Pilots could also add diversity to their job by rotating to serve passengers, if they so desired.
But the "people factor" is very important, some may wish to try it, others no.  First aid training and security, as well as diplomacy, would be talents required for stewards but would also benefit pilots.
All personnel on a passenger plane are vital components of a team, and some may find additional responsibilities a welcome improvement to their daily work experience.

Pretty sure that you need to be a pilot to be an FAA flight engineer, and there aren’t many airlines who have them.

@MichaelHall A flight engineer's license is separate from a pilot's license. There was no FAA requirement that an f.e. be a pilot unless the hiring airline required it. Back in the day when most large civilian aircraft had an f.e., many of them were licensed pilots or working on their pilot's license because the career path was f.e. first, then f.o., then captain. As the 3-man cockpit faded, a lot of the engineers were ex-military and had no pilot license. On the 747-100/200s that I flew in the 1990s, most of the f.e.s were not pilots.

Thanks for the perspective Terry.  I flew with enlisted flight engineers on the KC-130 and they always joked that they had no future on the outside.  Based on what you said, probably not because it was prohibited, but because they weren’t competitive due to the pipeline being full of pilots.  When I sought my ATP and was applying for flying jobs it was recommended and common to take the FE written to have a resume bullet.  I never did...  (Maybe why I’m not flying big iron today?!)

A former colleague was an FE on 747s in the early 90s.  He only had a PPL in addition to his FE license. so when the operator announced all dedicated FEs were being replaced with pilot Second Officers, he was on the outs.

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Are there any plans, designs, or prototypes for an electric ground effect vehicle?
I have been searching around for any plans, designs, or prototypes for a small GEV. All I have found is a ground effect gas powered like this link:

or an all electric prototype for short distance travel (not ground effect) at this link (eviation alice):

Are there any ongoing plans to build an electric-powered ground effect vehicle?
Would it be any better or faster than the current water taxi or ferry services?

The primary limiter is this: with batteries of current design, an electric GEV that can lift itself and travel a useful distance consists mostly of battery mass, with little useful payload. This is because a pound of jet fuel packs a lot more punch than a pound of battery.

so i guess if eviation alice short range plane is successful then that means there is enough battery energy density to do all electrics ground effect vehicle because high altitude flight takes more energy than ground effect flight right?

@user2177046 a good observation! Ground effect  flight indeed requires less energy.


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What engine power setting is used during cruise?
I am trying to work out what engine power setting is used during the cruise phase of commercial flights but I can't find anything about it in the usual spots. Anyone have any idea what percent of engine power is used? Like 50% engine power maybe?

I retagged your question because I assume that you're asking about typical airliner engine performance. "Commercial" is a very broad term that can include almost any aircraft type and covers a lot more than airline flights. If my assumption was wrong, just change the tags again as needed.

At first, I was tempted to close the question as a duplicate, but then I could not find one that would address the point directly. But there are many questions and answers on this site which allow one to cobble together the answer:

Why are many jet aircraft designed to cruise around FL350-370?
Why has the maximum service ceiling of Boeing and Airbus products remained about the same for 30 years?
Why do jet engines get better fuel efficiency at high altitudes?
How much fuel does it take to start/land an aircraft, compared to normal flight?
What is the one-engine-inoperative maximum range flight configuration?

To save you to read through all linked answers, here is the gist of it: Jet engines are run at close to their maximum power during cruise, but their thrust is much less at altitude due to lower air density. Airliners want to fly as high as possible to fly faster for the same drag and to gain efficiency, and their designs are balanced to achieve reasonable take-off distances and good cruise performance at close to maximum thrust.


text:
How do civil aircraft flying in formation handle ATC?
I assume that while en route, one aircraft could simply pick up flight following and the others do not need to talk to ATC, but what about upon reaching an airport? Do they simply announce "flight of xxx 10 mi east with W for full stop" and get successive landing clearances, or do they all break apart before getting close to the airport? Thanks!

As long as the aircraft are in formation, they are controlled as a single aircraft.
From US DoT OrderJO 7110.65T ATC General Control:

2-1-13. FORMATION FLIGHTS
a. Control formation flights as a single aircraft. When individual control is requested, issue advisory information which will assist the pilots in attaining separation. When pilot reports indicate separation has been established, issue control instructions as required.

The decision to break the flight lies with the pilot in command, and the ATC then controls the aircraft individually.

Separation responsibility between aircraft within the formation during transition to individual control rests with the pilots concerned until standard separation has been attained.

Upon break-up of the formation flight, the controller initiating the break-up shall ensure that all aircraft or flights are assigned their proper equipment suffix.

Also note the entry in the Pilot/Controller Glossary, which says Formation Flights "operate as a single aircraft with regard to navigation and position reporting".

Would they address the leader by tail #/call sign, or would they address the flight somehow with a flight identifier?

@Ryan, it seems to be common for military or ex-military members (whether pilots or ATC) to refer to formation flights as "Callsign 123 flight" on every transmission. I do not believe this is required for civilian aircraft or controllers and I do not do it; I just refer to them as the proper callsign. In either case, the leader speaks for the flight as a whole, so the callsign used is the callsign of the leader (until break-up anyway).

FWIW, back in the 1990s, on initial callup to a ATC frequency, we would say "N1234 flight of 2".

Do they simply announce "flight of xxx 10 mi east with W for full stop" and get successive landing clearances, or do they all break apart before getting close to the airport?

It is up to the pilots.
As aeroalias said, formation flights are considered a single aircraft and are controlled as such (although there is additional separation added: either "standard separation plus one mile applied to the lead aircraft" for a standard formation, or "standard separation applied in front of the lead and behind the tail aircraft" for a non-standard formation).
With regards to runway operations (takeoffs and landings):

A formation flight is cleared for takeoff once. It is up to the pilots to decide whether they take off single-file and join up when airborne, or take off as a group, or two at a time side-by-side, or what. This will depend on the skill and proficiency of the pilots as well as the type of aircraft; a formation of A-10s and a formation of Cherokees will be quite different.
A formation flight is cleared to land once. Again, responsibility for aircraft safety lies with the flight lead and the rest of the pilots, and they may elect to all land at the same time, or in a line, or successively by virtue of an overhead break maneuver.

The controller is not responsible for spacing the flight elements so as to provide same-runway separation between them unless they begin issuing control instructions to individual elements of the flight.
If the pilots are uncomfortable landing as a flight, they can request to break up and the controller will then issue appropriate instructions to separate the elements of the flight. For an IFR flight this will likely be diverging headings; for a VFR flight it could be direction-of-flight, S-turn, or 360º-for-spacing instructions. Once the elements have broken up the controller will issue individual landing clearances and ensure proper runway separation.
Note that "An aircraft conducting an overhead maneuver is VFR and the IFR flight plan is canceled when the aircraft reaches the “initial point” on the initial approach portion of the maneuver" (7110.65 3–2–10d).


text:
What's the definition and the meaning of “soft dirt runway”?
What's the definition and the meaning of "soft dirt runway"? You can read that expression in the following text:

..The aircraft's rolling resistance, μ, is determined by the type of
  runway surface and by the type, number, inflation pressure and
  arrangement of the tires. A thin, high-pressure tire operated over a
  soft dirt runway will have so much rolling resistance that the
  aircraft may be unable to move. A large, low pressure tire can
  operate over a softer runway surface but will have more aerodynamic
  drag if not retracted, or will take up more room if retracted. Values
  of μ for different runway surfaces are provided in the detailed
  takeoff analysis in Chapter 17. ...

Source: Daniel P. Raymer, Aircraft design: a conceptual approach. Chapter 5 Thrust-to-weight ratio and wing loading, paragraph 5.3 Wing Loading, sub-paragraph Takeoff Distance, page 88.

It sounds like a description of relative hardness. I don't think a specific definition is needed, as it appears he's just trying to create an example to show how a software runway would need a different tire setup.

@Steve Software runways are only found on flight sims :)

Err... Walk out on the runway.  If your shoes are leaving obvious tracks, it's soft.

The are many types of runway. But the basic are paved, unpaved. Paved runway may be in form of rigid and flexible. Rigid is one which is made of concrete.Flexible runway are made of like bituminous. And the soft runway is one which is not paved. The runway may be on ice sand or water. But generally for a soft runway we can assume it as a grassy runway.    I did not find anything specific about the dirty runway. But in general we can think dirty means the runway conditions which are not so good for the engine when using of reverse thrust , applying brakes or maintaining direction while on take off roll.

Not so.  I assume by "like bituminous" you mean asphalt paving?  Those are paved runways, just as concrete ones are.  There is also a major difference between a grass runway and a dirt one, this difference being that one is covered with grass (usually mown short), the other is bare dirt.  The OP asks specifically about "soft dirt".


text:
What is the difference between landing weight and end-of-mission weight?
Raymer says:

Landing is much like taking off, only backwards!....Note that the aircraft weight for landing analysis is specified in the design requirements, and ranges from the takeoff value to about 85% of takeoff weight. Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency.

What is the meaning of the last sentence: "Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency"?
How is the aircraft design is affected by such different needed kind of weight?
(Source: Raymer: Aircraft Design – A Conceptual Approach Chapter "17 PERFORMANCE AND FLIGHT MECHANICS" Paragraph “17.9 LANDING ANALYSIS ”)

If you're landing backwards, you probably shouldn't be flying in that strong a headwind!

End-of-mission is a time- (and case) dependent term. Your mission could end under a variety of circumstances. If your mission is to carry passengers from point A to point B and you have an uneventful flight, then end-of-mission and landing are the same thing. But (as stated above) if you have an emergency at some point, you might need to abort the mission. If this happens, then you are likely to end-up dumping as much fuel as necessary to get to your landing weight, because said end-of mission weight and landing weight will not be the same.
Here is an oversimplified example:
Aircraft AC has MTOW of 100,000 kg and a MLW of 50,000 kg. The same aircraft has to get from point A to point B, without releasing cargo or ordnance. During the mission AC burns 100 kg of fuel per minute. Ten minutes after departure the pilot realizes that he has forgotten his watch and needs to land immediately. Now after 10 min flight AC weighs 99,000 kg. Since the mission is about to end before MLW is reached (99,000 ~= 50,000), the captain can either dump some fuel or circle around until AC's weight is at most equal to MLW.

Thank you Peter Hristov, so how does this difference affect the deisgn for weight or for weight?

If you take the example of a fighter or reconnaissance aircraft the difference is apparent, lets take the reconnaissance aircraft, the mission could be map out section y of country z. In this case you have the take-off weight, fuel used during the flight to the mission, start of the mission (maybe supersonic) then the end of the mission. Finally you fly back to base and land.

If it's a commercial passenger flight, "end-of-mission" might be considered docking at the jet-way or hard stand, and shutting down the engines. Depending on what airport you land at, which runway you land on, and what gate you park at, a fair amount of fuel could be burned during taxi, therefore "EOM" weight would be less than landing weight.

@d.pensopositivo Maybe the most significant alteration would be the requirement for a fuel jettison (dumping) system. As you add equipment on board, your weight will inevitably creep up. Take a look at FAR 24.1001, FAR 25.119 and 25.121. Of course some large aircraft do not have FD systems and thus the popular loiter in a case of emergency occurs.

I'm still not understanding the logic of the line of reasoning of this sentence :  "Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency.''. What doest it mean? Does it mean that If L. W. is the same of E.O.M. weight when landing, the aircraft have to dump a lot of fuel?

Be careful! E.O.M.W. is a variable, a function of time (in the simplest case), whereas L.W is a constant (or a range) for the given aircraft. As time passes E.O.M.W approaches L.W. If you happen to have to land before E.O.M.W. = L.W. (notice the order in the equation), you might have to dump some fuel.

In the last sentence of your answer, shouldn't that be "...is at most equal to MLW"?

Well spotted. Thank you! Can't edit it for some reason, though.

@d.pensopositivo: The mission can end before landing if it has to be aborted due to an emergency; if the aircraft is still above its MLW at that point, it needs to dump fuel, loiter, or make an overweight landing.  The mission is everything that's planned for the aircraft to do, ending with a planned normal landing; if things go right, the EMW and LW are indeed the same (since the mission ends with the landing), but, if the mission has to be aborted midflight, the EMW is the weight at the moment the abort is called, at which point the aircraft is still in the air and yet to land.


text:
For jets, how can we show that 1/2*ρ*V^2 is equivalent to 1481.3*δ*M^2?
In Roskam's book, we find the following relationship given for climb performance in jet aircraft:

Thrust requested = $D$ = $C_d \cdot (1/2 \cdot \rho \cdot V^2) \cdot S = C_d \cdot (1481.3 \cdot \delta \cdot M^2) \cdot S$

How can we show that $(1/2 \cdot \rho \cdot V^2)$ is equivalent to $(1481.3 \cdot \delta \cdot M^2)$?
SOURCE:
Author: Jan Roskam
Title:  Airplane Aerodynamics and Performance
Paragraph "9.2 CLIMB AND DRIFT-DOWN PERFORMANCE OF JET AIRPLANES"

See 14.3.4 and how equation 14.27 is obtained.

Using the Mach number definition $M=\frac{V}{\sqrt{\gamma RT}}$, the ideal gas equation $p=\rho RT$ and the atmospheric pressure ratio $\delta=\frac{p}{p_0}$:
$$ \frac{1}{2} \rho V^2 = \frac{1}{2} \rho \cdot \gamma RT \frac{V^2}{\gamma RT} = \frac{1}{2} \gamma p \cdot M^2 = \frac{\gamma \cdot p_0}{2} \cdot \delta \cdot  M^2 $$
With $p_0=2116.2 \text{lbs}/\text{ft}^2$ and $\gamma = 1.4$ you get the desired result.

Obviously this explains why only American companies know how to design aircraft properly. The rest of the world, using different units, would get the wrong answer ;)


text:
How high does a jet have to be to hear its radio call?
I am a student pilot and I am learning about radio signals/communication.
I am studying for a test and a practice questions states:
You are flying circuits at a small airport and are flying at 1800ft ASL in the circuit (1000ft AGL) when you hear a radio call from a commercial jet at an airport 123 nautical miles to the south. Roughly how high does this jet need to be so that you can hear his radio call?
The only reference I can think of is that VHF signals can be heard by using a formula of:
Nautical miles = 1.23 * √ height above ground level. The answer would be 10000 ft (AGL)?, but I am not sure if that is the right formula to use or how to figure it out.
Please help.

The formula you're using is correct, but don't forget your own altitude.
$$d = 1,23 × (\sqrt{h_1} + \sqrt{h_2})$$
So in your case:
$$123 = 1.23 × (\sqrt x + \sqrt{1000})$$
$$100 = \sqrt x + 31.623$$
$$\sqrt x = 68.377$$
$$x = 4675\ \mathrm{ft}$$

Your answer looks right once I stop thinking you're an idiot because you used commas where decimals go ;)

Culture differences.. We use comma as decimal marker in Finland.

@Sami Then note that this is language-dependent, not culture-dependent ;-)

I just want to clarify that I didn't actually think you were an idiot. The commas did confuse me at first though. Was just trying to be funny, but upon re reading my own comment, it wasn't 100% clear I was joking.

@Greg Taylor No worries, I assumed you were :)

@yo' Bad choise of term on my behalf. Regarding computer user-interfaces and programming 'culture' is a set of rules for decimal markers, date formats, currency symbols etc.


text:
How much impact can be taken when flying in formation?
This recently published 360-degree video shows four F/A-18 Hornets performing impressive maneuvers what appears to be only a few inches apart.
Considering the risk of impact I find it hard to believe that a very slight contact would lead to immediate disaster.
Is this true? Assuming no damage is caused to the aircraft, how much impact can be handled (somewhat) safely?

I don't believe that any contact is considered acceptable, and any that would occur would have far too many variables to determine ahead of time what would happen.

The distances may be greater than you realize. Looking at two aircraft from the ground, it is not always easy to tell how much further away from you one of them is.

@DavidK The video was taken from within the cockpit of one of the airplanes flying in formation, and towards the end of the video the commander states that the "published" distance is 18", but that during some of the maneuvers they get as close as 6".

@Lnafziger Next time I suppose I should watch the whole video rather than just looking at the pictures.

@Lnafziger is correct that absolutely ZERO contact between aircraft flying in formation is acceptable, with Aerial Refueling (AR) being the sole exception to this -- but in that case the AR equipment is designed to allow for what's going on.
The problem with contact IS the significant risk of damage to the aircraft involved, so the assumption in "assuming no damage is caused, how much impact..." is outside of typical experience.  IF you could assure no damage, then all sorts of things might be possible, but even pretty stoutly built fighter jets still aren't "bumper cars" and shouldn't be treated as such.  Even if a collision didn't cause an immediate structural failure, the risk of damage to the internal structure of the wing/tail/whatever would be enough that the aircraft would have to be taken apart & xray'd (or another non-destructive inspection method) to ensure that there wasn't damage that would later result in structural failure.
The one exception to all of this that I can recall was a technique that the RAF used in WW II to defeat the V-1 "buzz bomb" cruise missiles.  While the Spitfires could shoot them down, the small size of the missile meant that you had to get so close that you were probably flying through a cloud of debris right after you killed it (i.e. the warhead would detonate and the shrapnel might bring down the Spitfire as well).  They discovered that the gyroscopes in the V-1 guidance (i.e. the primitive autopilot) would tumble if they were inverted, so some pilots would fly formation with the V-1 then intentionally make contact with its wing with their own, flipping the buzz bomb onto its back.  At this point, the autopilot lost its bearings and the V-1 went down into (presumably!) empty countryside, crashing far from its London target.
Other than this, formation flight is carefully planned out so as to minimize all risk of contact between the aircraft.  Even in the (very cool!) video of the Blue Angels, you can see that there is always space between the wingtips -- more space for the more dynamic maneuvers, with the least space during a fairly brief and reasonably stable pass.  Remember, these pilots are extremely good & highly experienced in this sort of formation flying, and while there IS oscillation in pitch & roll, the formation is designed so that this can safely go on.  There just isn't much risk there of a force that would move one aircraft directly to the left or right of its position. Turbulence might produce a rolling or pitching motion that could LEAD TO a collision, but the pilots have enough control authority to correct these sorts of forces.
That's why they're able to do what they do, safely.
Fly Navy!

Willy Coppens deliberately touched his Hanriot HD.1 down onto an enemy balloon during the First World War. Does that count as contact between aircraft? Of course, the primary contact would have been with his landing gear, which after all are designed to contact another object.

Doesn't sound like formation flying there, but an interesting story.  Intentionally ramming an enemy aircraft has been used as a tactic, but that's entirely different than the topic of contact between aircraft flying in formation with one another.

The buzz-bomb tactics, not formation flying, reminded me of the balloon-busting story. It's still not even the same as that, because while Coppens actually "landed" on balloons twice, in neither case does it seem the contact was an offensive move.

small detail: the Germans caught on to the wing flipping of the V1 and added contact triggers to the wingtips that'd detonate the V1 when the action was attempted.

It should be noted that the Blue Angles is the most dangerous assignment that an airman can have. I believe that their fatality rate is something like 10%, that is, 1 in 10 Blue Angles pilots has been killed in a Blue Angles mission.

The V1 wing tipping procedure was a non-contact procedure, the intercepters wing was brought to within 6 inches below the V1 wing. This was sufficient to alter airflow over the V1 wing and destabilise its flight.

@dotancohen A very sobering statistic. I wonder how the Blue Angels compare to other units in deaths per flight hours. I did search for those numbers but couldn't find them easily.

As a counter-example, in this incident from the Vietnam air war https://en.wikipedia.org/wiki/Pardo%27s_Push one jet fighter used its canopy to push on the tail hook of another, damaged fighter, extending its range to exit enemy airspace...

Blue Angels fatality rates are not even close to being as high as you suggest.

During formation flying, no contact is acceptable. At the speeds of demonstration, any contact will be dangerous.
During formation flying, the pilots take every precaution to prevent accidental contact, including preventing accidental movement of control stick. According to Commander Shaun "Linus" Swartz of Blue Angels,

The Blues attach a 40 lb spring to the stick in the jet. This spring applies 40lb of nose down stick pressure, so to fly straight and level each pilot is essentially doing a 40lb curl. The purpose of this is it takes out the slop in the stick (imagine driving down the street in your 1965 Ford F-100 and the wheel moves +/- a couple inches left or right without the truck actually moving, same thing happens in a jet, and you can't have that flying a few feet apart).

As an example of what will happen if there is contact during formation fling, consider the crash of two Il-38s in 2002. During the ceremonial fly past, the wings of the two two aircraft brushed against each other, resulting in the death of all flight crew and another 3 on ground.
During formation flying, even flying into the aircraft wake can be dangerous- like the XB-70 Valkyrie crash. Note that in both these examples, the aircrafts were flying in same direction.
In summary, no contact is permitted in formation flying and pilots take every precaution against that.


text:
Windowless VS windowed aircraft
While Emirates was showing off its triple seven's ability to provide crystal-clear viewing from virtual windows, it mentioned: "that could be a step to windowless aircraft", and I felt like it meant to evolve into something better.
So, my question is, what would be better in general, a windowless aircraft or one with windows? Is there any improvement that comes with a windowless Airbus for example?

Would be great to have one post to cover all scenarios though, and link to them for further link, maybe..@ymb1 thanks!

I'd argue that this isn't a duplicate question; the linked question is asking specifically about the drag factor and has answers explaining only that. This question is asking for an all-round view of other factors - passenger comfort, cost, etc.

As far as I know, a windowless aircraft made with the right materials would be better than one with windows since in current airliners are weaker than the rest of the fuselage. With uniformity in the fuselage, the chances of weak points would be less.
From a structural point of view, windowless > windowed aircraft.
This is as much as I can say since my knowledge on the subject is limited.

Good point, though all this technology of video streaming would be an overhead, but maybe negligible..

Video streaming is a potential workaround to finding a material/ set of materials that would work as the main material of the fuselage while also being transparent enough to see out of clearly. I'd wager that video streaming will be the way to go for windowless aircraft at least for the next few years until they find a suitable replacement for the fuselage material. Airbus does have a windowless concept as seen here: http://www.arabianbusiness.com/from-bigger-faster-windowless-planes-escape-pods-pilotless-cockpits-virtual-reality-entertainment--future-of-aviation-586965.html

https://www.theguardian.com/notesandqueries/query/0,5753,-43290,00.html This is actually a good discussion that relates to your question.

There are two big advantages to windowless aircraft:

Cost
Design complexity/structure

Cost is a fairly obvious one; the plexiglass used for aeroplane windows is not expensive, but designing around it increases costs all the way from conception to manufacture of an airliner. Plus the airline needs to think about blinds/curtains, seat placement, and the extra processes involved in cleaning all the windows on the aircraft regularly - inside and out.
To the second point: design. Not only do windows complicate the design of an aircraft (thus increasing the cost) but they're also structural weak points. An aerospace engineer would like nothing more than a simple tubular fuselage without these vulnerable stress points (aircraft windows are round rather than rectangular to reduce these).
Here's an interesting example of a windowless concept aircraft: the Reaction Engines A2. This hypersonic aircraft flies so high and so fast that the stresses and heat on the fuselage are simply too much for big windows to handle. Any windows would have to be tiny (like on Concorde) - so they're simply left out.
So to sum up: windowless aircraft certainly an option for future superfast and high-altitude air travel, but for today's commercial airliners the only point would be a slight saving in cost. Whether the idea of a windowless airliner would affect passenger number is unknown, but I imagine a lot of people would be uncomfortable with the idea.

I miss the Concorde. Or maybe I miss that there is no successor to it. Thanks!


text:
How to do Weight & Balance for Cessna 172?
What is the best method to do Weight & Balance for a Cessna 172? (If it's possible with a small tutorial!)
Thanks

The Calculation section of “Center of gravity of an aircraft” on Wikipedia gives an overview of the steps.

Determine the weights and arms of all mass within the aircraft.
Multiply weights by arms for all mass to calculate moments.
Add the moments of all mass together.
Divide the total moment by the total weight of the aircraft to give an overall arm.

The Basic Empty Weight (BEW) of the aircraft will come from the Weight & Balance information that is unique to each aircraft. The computed arm for the BEW may have some rounding error, so treat it as informational. Use the precise figures for Weight and Moment from your aircraft’s W&B.
The arms, distances from some reference datum, will also come from your aircraft’s W&B info: fuel, front seats, rear seats, and baggage areas on a Cessna 172. Copy those into your table as well.
Avgas (100LL) weighs 6 pounds per gallon, so the weight is 6 times the number of gallons.
I like to work top-to-bottom and left to right. For the grand finale, divide the sum of the Moment column by the sum of the Weight column to get the overall center of gravity.
The example below is from my PP-ASEL checkride taken in a Cessna 172. The items in boldface are computed values. The digits after the decimal are there for typographical purposes and do not necessarily indicate significant figures.
$$\begin{array}{c|r|r|r|}
                     & \textit{Weight} & \textit{Arm} & \textit{Moment} \\ \hline
\text{Airplane}      & 1{,}665.6     & 39.2       & 65{,}928.93      \\
                     &               &            &                  \\
\text{Fuel (50 gal)} & \bf{300.0}    & 48.0       & \bf{14{,}400.00} \\
                     &               &            &                  \\
\text{Bacon}         & 180.0         & 37.0       & \bf{6{,}660.00}  \\
\text{Shelton}       & 172.0         & 37.0       & \bf{6{,}364.00}  \\
                     &               &            &                  \\ \text{Duffel}        & 10.0          & 73.0       & \bf{730.00}      \\
\text{Shelton bag}   & 10.0          & 73.0       & \bf{730.00}      \\
                     &               &            &                  \\
\text{Backpack}      & 15.0          & 93.3       & \bf{1{,}399.50}  \\ \hline
                     & \bf{2{,}352.6}& \bf{40.9}  & \bf{96{,}212.43}
\end{array}$$
In this particular case—given for information only—the center of gravity (40.9 ≈ 96,212.43 / 2,352.6) at the total weight is within limits for the Normal category as given in the aircraft’s Pilot Operating Handbook (POH). Your case may vary. The Pilot-in-Command is responsible for computing Weight & Balance for each flight.
As a point of interest, my DPE was Clyde Shelton who recently flew his ten thousandth checkride.

Shouldn't you also add the weight of the pilot and passengers?

@ROIMaison Yes, the pilot in this case is the row labeled Bacon, and Shelton was the one passenger.

Ah right, I was looking for something along the lines of passenger, and completely missed the names!

Aircraft weight and balance is done the same for all aircraft (at lest all GA aircraft as far as I know). This PDF from the FAA provides a nice overview of it. You will need a few of the constants out of the POH for your plane such as dry weight and moments for various things. As well as specifics from your airplane is other avionics have been installed. Other than that this walkthrough covers it pretty well.


text:
What does the snowflake with temperature symbol on an approach plate mean?
I've only seen the snowflake symbol with temperature listed on this one approach plate for KASE airport in Aspen, CO. I looked for it in the legend but didn't find it. Does anyone know what the snowflake symbol with temperature means?

From FAA INFO 15002:

A [snowflake] -XX°C icon will be incrementally added to airport approach plates, beginning Mar 5, 2015. The
  icon indicates a cold temperature altitude correction will be required on an approach when the reported
  temperature is, “at or below” the temperature specified for that airport.

This looks to be a work-in-progress, as they started adding the icons in March, and compliance with applying the cold temperature altitude corrections becomes mandatory in September, 2015.
More info from the NBAA:

Background: In response to aviation industry concerns over cold weather altimetry errors, the FAA
  conducted a risk analysis to determine if current 14 CFR Part 97 instrument approach procedures, in the
  United States National Airspace System, place aircraft at risk during cold temperature operations. This study
  applied the coldest recorded temperature at the given airports in the last five years and specifically determined
  if there was a probability that during these non-standard day operations, anticipated altitude errors in a
  barometric altimetry system could exceed the Required Obstacle Clearance (ROC) used on procedure
  segment altitudes. If a probability, of the ROC being exceeded, went above one percent on a segment of the
  approach, a temperature restriction was applied to that segment. In addition to the low probability that these
  procedures will be required, the probability of the ROC being exceeded precisely at an obstacle position is
  extremely low, providing an even greater safety margin.
Action:
  Pilots must make an altitude correction to the published, “at”, “at or above” and “at or below” altitudes on
  designated segment(s) (see list below), on all published procedures and runways, when the reported airport
  temperature is at or below the published airport cold temperature restriction.
Pilots without temperature compensating aircraft are responsible to calculate and make a manual cold
  temperature altitude correction to the designated segment(s) of the approach using the AIM 7-2-3, ICAO Cold
  Temperature Error Table.
Pilots with temperature compensating aircraft must ensure the system is on and operating for each segment
  requiring an altitude correction. Pilots must ensure they are flying at corrected altitude. If the system is not
  operating, the pilot is responsible to calculate and apply a manual cold weather altitude correction using the
  AIM 7-2-3 ICAO Cold Temperature Error Table. PILOTS SHOULD NOT MAKE AN ALTIMETER
  CHANGE to accomplish an altitude correction.
Pilots must use the corrected MDA or DA/DH as the minimum for an approach. Pilots must meet the
  requirements in 14 CFR Part 91.175 in order to operate below the corrected MDA or DA/DH. Pilots must
  see and avoid obstacles when descending below the MDA.
The temperature restriction at a “Cold Temperature Restricted Airport” is mutually exclusive from the charted
  temperature restriction published for “uncompensated baro-VNAV systems” on 14 CFR Part 97 RNAV
  (GPS) and RNAV (RNP) approach plates. The charted temperature restriction for uncompensated
  baro-VNAV systems is applicable to the final segment LNAV/VNAV minima. The charted temperature
  restriction must be followed regardless of the cold temperature restricted airport temperature.

There's more info in the NBAA document (I only included the exciting parts), including a list of affected airports, listed by state.  Lots in Alaska, none in Florida, unsurprisingly.  Applying this in flight looks like an absolute can of worms, as far as I can tell from the examples presented.
We'll probably see more come out about this as cold weather approaches, so stay tuned!

It indicates a "temperature restricted" airport where precautions are required to calculate and set correct altimeter settings because the errors caused when the temperature is at the lowest recorded , if not corrected, can exceed the required obstacle clearance shown on the chart.
Since the air is significantly more dense than the "ISA standard day", the altimeter can over read (the pressure for a given altitude will be greater), telling you that you are higher than you really are with a risk of ground or obstacle collision.
If the temperature is at or below that shown on the chart, altitude corrections must be made.
Full details can be found at 4-GEN-14 of the FAA NOTAMs.

did you not mean to say "(the pressure for a given altitude is LOWER) telling you that you are higher than you really are..."?


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What would the ranks most likely be of the crew of a B-1B?
I'm currently attempting to write a novel which briefly features a modified B-1B undertaking a risky, highly important mission in support of a Special Access Program. Since a few scenes are set in the cockpit and feature a discussion between the crew, it would be very helpful to know what the ranks of the crew would most likely be.
I've done a little research via a number of sites and e-book previews but so far I've not turned up much other than at least one Lancer pilot who was a Major but I have no idea how the co-pilot, DSO and OSO would compare in rank, or if B-1B pilots of greater rank than Major would be realistic/believable.

Welcome to aviation.se!

See this WSO Page for a short paragraph discussing ranks

In general, the pilot could be a captain, major, or lt col, the copilot probably a 1lt or captain, and the navs any of the above. For a select crew handpicked for a "fate of the world" mission, you might put 2 instructor pilots together along with two senior navs, so all 4 as lt cols wouldn't be impossible. On the other hand, if the crew is essentially detailed off to be "secret squirrels" for a while, it probably wouldn't be stacked quite that high, so maybe a mix of majors & captains. That happens because it quickly becomes disruptive to take senior guys (tactics officers, instructors, the ops officer or commander, etc) away from their regular squadron jobs for a prolonged period. The more important the mission, the more that disruption is accepted.

Definition: "the most dangerous crew combination" - 2 instructor pilots. Tongue-in-cheek, yes. But deadly serious. Relaxing one's vigilance because you assume the other guy knows what hes doing, and the other "pushing it" assuming you will keep him out of trouble. The combination may forget skills and egos never trump the laws of physics.


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Why is the B787 one of the few aircraft with electro-thermal wing anti-/de-icing?
While I was searching for a listing of aircraft with different anti-/de-icing methods - especially for electro-thermal wing anti-ice - I couldn't find any information about other aircraft except the B787.
Is there any reason, why other methods like TKS or using bleed air were prefered in the past?
Are there any studies related to the pro's and con's of the different anti-/de-icing systems?

Just a hypothesis here, no hard facts: would the B787 be generally more reliant on electrics than hydraulics or pneumatics? Could it have more electrical capacity built-in as a consequence? If so, de-icing with electricity may be seen as a design simplification, which is always nice.

Partially because 787 has no bleed air available for any purpose. Its engines do not draw bleed air traditionally. Any pneumatic system draws air from other pumps. Hence electro-thermal wing anti-ice system is needed since no bleed air is available.

Engine anti-ice is still done with bleed air. http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_3.html

Traditional anti-ice systems use engine bleed air through the pneumatic system. Engine bleed air is air that is compressed by the engine compressor to high pressure. Due to thermodynamic effects the air also warms to fairly high temperatures. This air is then bled off the engine through valves to supply the aircraft's pneumatic system. The pneumatic air is then sprayed on the inside of the leading edge of the wing or engine cowl to prevent ice accumulation.
Engine bled is a very expensive source of energy on an aircraft because compressing air isn't that efficient, the engine core has to be slightly larger to accommodate the increased airflow, and the pneumatic system itself is typically one of the least reliable systems on the aircraft. The system also uses many large ducts that are heavy and take up a lot of space, which dictates larger passages in structure, which is more weight again. However, bleed air is available making it an attractive source of energy.
The 787, however, shed the vast majority of the pneumatic system (see the link Sports Racer posted above http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_3.html). This decreases the specific fuel consumption of the engines quite a bit. Reduces weight, and removes an very unreliable system from the aircraft.
The 787 is able to get away with this because it has very advanced electrical starter/generators. The generators can produce about 500 KW each, significantly more than any other Boeing aircraft. Since there is so much power available, electronic heater blankets for anti-ice are feasible, no other Boeing aircraft has the excess power to use electric anti-ice on the wings. Besides being much lighter, the electric blankets will use the energy more efficiently as well.
Although the generators still pull power off the engines, increasing fuel burn, the process is much more efficient than using bleed air.
FYI: The generators are also the engine starters, which eliminates another major pneumatic component on other aircraft.

As starters the same Generator functions as a motor?

Yes, @curious_cat, they are "starter generators" and provide both functions. Here's a link to a Hamilton Sundstrand press release that describes them.

The reason is that is is new.  The B787 is one of the few recent examples of an aircraft where the engineers were allowed to go back to the drawing board and really innovate.  It is therefore one of the only examples of a truly new generation of aircraft.  Most of the time when an aerospace engineer is asked to work on a new aircraft they are required, for many reasons, to draw heavily from “heritage” systems that have already been flight proven.  It is only when there is a demanding business case for entirely new designs, that an engineer is allowed innovate.  The B787 was intended to be a long range aircraft that would compete with larger aircraft (like the A380) that seat more people.  The idea was to offer more flights with the same or better per capita cost.  In order to make that vision a reality, the 787 had to be significantly more fuel efficient.  Which is why Boeing went back to the drawing board and redesigned the engine and the wing shape and relied heavily on composite materials so that the aircraft would be exceptionally light.
There are two huge changes that necessitate an electrothermal icing protection system: 1) the use of composites and 2) elimination of the bleed air system many others have mentioned.  Bleed air is, by definition, an inefficiency.  The system poaches hot air from the jet engines in order to prevent ice formation on the wings.  All of the energy used by the bleed air system would have otherwise been used to produce thrust.  And that hot air is much hotter than it really needs to be in order to protect the aircraft from ice accretion.  There is a big desire across the aviation industry to get rid of inefficient bleed air systems, however, these systems are integrated into the aircraft structure so they really can't be eliminated until a particular aircraft model is completely re-designed.  The B787 system is said to be 50% more efficient than a bleed air system would be (if on the 787).
The other factor I mentioned was composite structures.  The B787 is the first major airliner to be made largely of composite materials.  Composites make the aircraft lighter and therefore more fuel efficient.  As I mentioned before, bleed air is hotter than it needs to be to protect the aircraft from ice.  It is also hotter than most carbon-fiber composites can tolerate.  The hot bleed air is piped from the engine through the wings to the leading edges of the wings so there is a concern with composite aircraft of damaging the aircraft structure with extremely hot air.  Electrothermal systems eliminate this concern by applying heat only where and when it is needed and only with the necessary energy.  There are high-temperature composites but they are more expensive and given that bleed-air is inefficient it’s better to go with electrothermal.
We will see all major aircraft turn to electrically based ice protection in the future.  There have, indeed, been other “new” aircraft models since the 787 but it is all a matter of whether the business case for those models was strong enough to warrant a costly re-engineering and re-certification effort (e.g. with the FAA).  For example, a smaller 737 aircraft that typically travels within the same continent has less of a driving need for these efficiencies.  That said, Boeing has plans for all their models to be re-designed in the image of the ’87 when the time is right.  And other aircraft OEMs are making similar changes.


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What do the gyroscopes used in commercial aircraft actually look like?
I pretty much grew up watching Air Crash Investigation and Seconds From Disaster and every other episode had a mention of the aircraft’s gyroscopes, but I always wondered how did FAA rated industrial long use gyroscopes actually look like and where were they physically placed inside the aircraft?

This answer shows a pretty good cutaway.

Related: https://aviation.stackexchange.com/questions/38809/how-are-pitch-angle-and-pitch-rate-measured-in-an-airplane/38823#38823

The first gyros were mechanical: A spinning wheel with gimbal mount and driven by air pressure. The picture below shows the innards of one which was used in the Supermarine Spitfire (picture source). The black disk on the right is the instrument background and the arm on top moves the vertical needle sideways in accordance with the turn rate of the aircraft. The white coating on the needle is phosphor to make it glow in the dark.

State of the art is to use a ring laser gyro. This is an optical device which sends a laser beam around a triangular or square track in both directions. Rotations will make the light path shorter in one direction and longer in the opposite direction, so the interference between the two beams shifts the place where the waves cancel each other. This shift is registered and interpreted as a rotation. An alternative design uses optical grade glass fibers for the light path.
The placement is important because flexing of the fuselage will give different results for different mounting positions. To my knowledge, in airliners gyros are mostly part of the avionics suite below the cockpit.
See here for a list of sample applications.

Ring laser gyro assembly with three gyros, one for each spatial axis (picture source).
More modern MEMS sensors are on the advance but mostly to be found in backup systems or on unmanned aircraft. They are much more compact and use less power, but their accuracy is lower than that of ring laser gyros.

Silicon Sensing CRS03 MEMS gyro (picture source).

It'd be cool if you added an old style pneumatic gyro

Enjoyed the picture of the ring laser gyro. I never have actually seen one on an airplane. The one they showed us in A&P school for an early 747 looked more like a small washing machine or bicycle wheel and was said to have 2mi of optic cable wrapped in loops.

The Honeywell Aerospace LASEREF VI Micro IRS is one of the most common for recent commercial aircraft. Page 11 of the linked PDF has a pic of the actual RLG.

Modern 'gyroscopes' are miniaturized, solid-state acceleration sensors, that work sensing the vibration of a very small mass. With an instrument having three vibration sensors set up in three perpendicular directions, you can always infer the rotation of that instrument in relation to the 'absolute' space...

This doesn't seem to answer the question @xxavier

@GdD Well, it hints at how they actually look like...

Not really, I think the question is asking about what gyros actually look like physically, and not just solid state ones.

@GdD Well, may be that's your opinion... I have a different one...


text:
Is there any kind of removable ELT on board an airliner?
Is there any equipment similar to an ELT on board on airline airplanes as for GA aircraft? Something that can be removed from the wreck in the event of abandoning the site of the crash.

I know that there is the Flight Data Recorder that keeps giving signal to rescue teams, but in case that the wreck must be abandoned how could I be sure to be found?

Related, maybe duplicate (you decide): How is the emergency locator transmitter of the A320 fixed, activated and carried away?

I don't believe that general aviation ELTs are designed to be easily removable in the event of a crash.

@Steve Kuo for what I know the ELT is removable, in the aircarft that I fly (cessna 152/172) is positioned in a case inside the fuselage on left side, the screws for that case are made of plastic which make them easier to brake if they get stuck due to impact. But I have never tried to open so far.

@mins thank's for reply. Good stuff. I appreciate.

What do you mean by removable? Every ELT is removable to some degree, depending on means of installation. All ELTs that I have worked on could be removed with means requiring minor mechanical skill and bare hands or simple tools.

If you are worried about being located in case of a crash, buy yourself a handheld EPIRB. They can be brought with you on carry-on luggage and cost as little as $125 on eBay.


text:
What happens if a language other than English is used over the radio?
In many non-English speaking countries, communication with ATC may be conducted either in English or the native language. Famous examples are China, Russia, France and possibly Germany.
When a pilot who is a non-speaker of the native language hears such communication, which is he to do? Just sit back with no idea of what is going on?

Always wondered if forcing all people involved in aviation to learn an artificial lingua franca (e.g. Esperanto) would help to raise situational awareness.

Lojban would make a perfect language for that.

Germany? Did you experience that or is it just an assumption ("possibly") based on German being in the Top 10 of the most-spoken langauges world-wide?

I heard German was used in Germany in the past. I also read some where it is no longer applicable. Hence "possibly".

Cant help but must add this link. Get a Singaporean near your to help translate https://www.youtube.com/watch?v=3EjqHxLtwSQ. No offense to any nationality. Be proud of your identity!!

@orique, as far as using an artificial lingua franca, there are more Klingon speakers now than Esperanto.  lets use that instead.

@AndyDingfelder I'm not talking about count of speakers; rather about neutrality (i.e. not favouring people from certain nations) and ease of learning it.

@vasin1987: I'm pretty sure most Germans speak German...

During the 1990s I flew into countries on every continent except Antarctica. As an American English speaker flying U.S. registered airplanes, I never had a complaint that a controller had trouble understanding me, and I was always addressed in English by the controllers. Sometimes, though, I would have trouble understanding the controller's accent and would have to ask them to repeat their instructions.
As you mentioned, in some countries the controllers will address the pilots of that country in their native language. Personally, I always felt that compromised the smooth functioning of the system to a degree, because it denied a good bit of the overall picture of what was happening to the pilots who didn't speak that language. For example, if two airplanes preceding you are being rerouted for some reason, but you can't understand what they've been given (and which you're probably going to be given), you're not as prepared for the reroute when it comes through to you in English.
Even if controllers spoke to you in English, they would typically pronounce place names and fixes as they are pronounced in the native language. My first flights in France were a real problem in this respect. The French controllers were speaking good and understandable English, but the French pronunciation of the place names did not match our English rendition of the names we were seeing (and had never seen or heard before) on the IFR maps (no glass cockpits back then for us). In a couple of instances, we had to request that they spell the names, which didn't make us popular. On one occasion, when we made such a request, another pilot came on frequency and said, "He means ...." and gave us an English transliteration if you will of what the controller was saying.
Interestingly, the worst time I ever had understanding a clearance was one from a nominally English speaking controller. We were talking to Scottish control, and received a reroute into Amsterdam from a controller with a very pronounced accent (Glaswegian?). All I was able to get was that at the end he was turning us over to Dutch control and the frequency. I went over to the Dutch, and asked for them to restate what our new clearance was, and I apologized, explaining that I had been unable to understand Scottish control. His first words were, "That's okay, we can't understand them either."

Wow, this gave me a new view on language internationalization.

This has been my exact experience in France, and in South America. Fortunately I know basic Spanish, so am able to find their fixes with relative ease, but in France it is downright impossible, AND the French controllers will simply keep repeating it the same way over and over even though they know that it sounds completely different than it looks to an English speaker....  You have to ask them to spell it, which as Terry says, annoys them.

At Schiphol, KLM and Transavia pilots get the Spijkerboor approach assigned and the rest the Sierra Papa Yankee approach. I always like to think that foreign pilots believe that the Dutch get a priority straight-in approach, while they are of course the exact same.

At least ATC speak "good and understandable English". I'm not sure native english-speaking (lets say over Texas) would make an effort to do so if not requested to repeat slowlier by a non-native.

At international  scientific conferences where English is the lingua franca, I have found something similar. Native speakers of English are often harder to understand because of their larger vocabulary and collection of idioms. This is compounded by their speaking in some regional accent, which can render their talk almost unintelligible.

Don't worry, we Brits can't understand Glaswegians either....

In a non-piloting situation, I once could not understand a person's pronounciation of a letter of the alphabet (they pronounced "h" like "hatch"). Combined with the need to spell things out sometimes, we can see how the phonetic alphabet is critical for reliable radio communication ("hotel" would have been so much clearer).

Another similar anecdote I've heard is over Israel, controllers and pilots alike may be speaking Hebrew until the moment an English-speaker comes onto the frequency, at which point everyone seamlessly transitions to English.  I can't confirm this story personally, but it seems reasonable.

This is much more common than just the countries you list.  In Mexico, for example, ATC communications with Mexican carriers are entirely in Spanish and many of the controllers have thick accents.
Thankfully, ATC phraseology is standardized and limited in vocabulary so it isn't too difficult to get the basic idea of what is going on.  If you pick up on the words for "left", "right", "climb", "descend" and the numbers you'll maintain a good idea of what other airplanes around you are doing.  The corollary to this is the controllers often get by in English the same way.  I once tried to report an un-tethered balloon floating up near our position and going "off-script" made it hard to communicate.  In the end an AeroMexico pilot translated what we were saying to the controller in Spanish.
One thing you don't want to do is decide, once you've learned the words for "hello", "good morning", etc, is to use those during your initial callup to foreign ATC.  It might sounds nice to say "Buenos dias Monterrey, jetlink treinta treinta-dos nivel do veulo tres siete cero" but  it'll backfire on you when the controller responds in Spanish.  This is doubly true in Canada where the controllers (particularly over Québec) are quite happy to service you in French.

Of course, controllers (anywhere) similarly complain about pilots not being able to speak much English when they need to go “off-script” (e.g. to ask for rate of climb or something like that).

Basically, yes.  This is also common in most of the Spanish speaking countries that I have flown within that are in the Americas, as well as French being predominately used in France.
In each of these places it is very common to hear ATC speaking to many (most) of the pilots in their native tongue, and speak English only when talking to someone that doesn't speak it. (Sometimes with a very strong and hard to decipher accent.)
I prefer being able to hear everything (sometimes you can catch things that you might not otherwise), but that's just the way that it works.

The ATC will repeat to you whatever he deems necessary for you to know. All transmissions "to all stations" will be also in English. Private pilots may not even posses the aviation English certificate (it is an optional extra course in our country) and they still want to be able to fly.
If you are a pilot of a small airplane yourself, it may even happen to you that the  AFIS or RADIO station at the local airport doesn't have the English certificate and will not be allowed to advise you in English.

Why is it a community wiki I have no idea.

It looks like you ticked the "community wiki" box when you posted your answer.

Seems to be the case, I was sending the answer from my mobile phone.

In Brazil, ATCos communicate on their native language (Portuguese) or in English. If you do not speak English, it will not be recommended do fly across your boundaries.

I don't fly but I would guess it would be the same as computer programming.  The pilots probably learn a set of commands that ATC will give them, these commands will be a standard set around the world, so it won't necessarily be "English" that is spoken on the radio, more an international code language.
When I did amateur radio we had various Q-codes and number codes like 73's, 88's, QTH, QRZ - all these meant the same no matter which country you were from and that way we could speak to each other regardless of language, and it was it's own language known mainly by the amateur radio community.  I would guess that pilots have the same thing - for example in amateur radio the following would mean
1: QTH?
2: QTH Berlin"
1: Where are you?
2: I'm in Berlin
I don't know whether pilots use Q codes but I guess they must have something similar to this
Also there has been other things that have used these radio codes - for example the messenger service ICQ was named because the code for calling for a response on radio is to CQ ("Seek You") someone - "CQ, CQ, this is GW0AAA /MM calling CQ" means that someone with the call sign of G0AAA is in Wales on a boat of some sort and they're calling out to anyone who may be interested in having a chat (also the callsign gives you additional information about the person your speaking to - I assume pilots have similar things a callsign that starts G or M indicates that the persons amateur radio licence is from the UK, the second letter is used to indicate which part of the UK the person is calling from - England doesn't have a secondary letter but Wales has W, Scotland is M, NI is I, IoM (D), Guernsey (U) and Jersey (J) are also included even though technically they're separate from the UK with their own government) and the end bit also tells the person even more information - for example /M = the person is mobile, /T they're in a temporary location, /MM is maritime mobile, etc - but with all that extra information you don't really need to know English to work out roughly where that person is.
And finally with modern translation services and computer systems I would also guess that anything that comes through the radio now on a plane would also probably be sent to a screen on the dashboard, which has the ability to translate - just a guess but can't see why this isn't incorporated into planes (it is on Microsoft Flight Sim and that's supposed to be "As Real As It Gets!" - although I have heard that XPlane is much more real!) - and it wouldn't need to be a very big dictionary of words either for translation because there would only be a select number of phrases you'd need, your not really going to sit there and have a full on conversation with ATC are you - both them and you want to keep communication short and to the point because other people also need to use the radio comms.

These are just guesses, but the answers from some experienced guys above, who do fly or control (not me), explain it better. Pilots use preset phrases, but it is normal speech, be it English or some other language. There are Q codes in aviation (QNH, QFE, QDM), but their usage is limited, you cannot control airplanes just using them. Finally, radio is just radio, you speak to a microphone and listen to the headphones. There is no magical translation to something on the dashboard. Especially not in small planes. Aviation is NOT just large scheduled passenger jet traffic.  Why so many guesses?

I spent 18 years doing software development in Fortran, Cobol, PL-I, C, and a number of machine dependent assembler level languages. Then I switched careers and flew aircraft ranging from light single-engine to 747s. On the basis of that experience, I can assure you that the communication between pilots and controllers is not equivalent to computer programming. Negotiation and nuanced language is often necessary. Sometimes you tailor what request to such things as the tension in the speaker's voice or how fast they're speaking. For these things you need a spoken language, at least for now.

authors: Vladimir F Героям слава


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What is the fuel/air ratio of the CFM56-5A1 engine (in the A320 model)?
I could find the fan-bypass ratio, which was 6:1 (on some models 5:1) but I was unable to find the fuel to air ratio used in this engine. For reference, it is a high-bypass turbofan engine.

I don't think I've ever seen it quoted directly, but if you get calculate it from the mass flow rate, fuel flow rate and bypass ratio.

The ratio can be different for different phases of flight. It is easy to calculate for the Takeoff (TO) case because the required numbers are easily available:

TO Thrust: $ 25 \, 000 \, \text{lbs} $ [1]
TO TSFC (thrust specific fuel consumption): $ 0.3316 \, \text{lbs/h} $ per $ 1 \, \text{lbs} $ of thrust [2]
Airflow: $ 852 \, \text{lbs/h} $ [1]
bypass ratio: $ 6.0 : 1.0 $ [1]

The takeoff fuel flow $ \text{FF} $ is then given by
$$ \text{FF} = 25 \, 000 \times 0.3316 \, \text{lbs/h} \approx 8290 \, \text{lbs/h} \approx 2.30 \, \text{lbs/s} \approx 1.04 \, \text{kg/s} $$
and the airflow $ \text{AF} $ through the core is given by
$$ \text{AF} = \frac{1}{6 + 1} \times 852 \, \text{lbs/s} \approx 122 \, \text{lbs/s} \approx 55.2 \, \text{kg/s} $$
This results in a fuel/air ratio of
$$ \frac{\text{FF}}{\text{AF}} \approx \frac{1}{52.9} \approx 0.0189 $$
Sources:

[1]: www.cfm56.com
[2]: Wikipedia CFM56

"Fuel/air ratio" would normally refer to a stoichiometric value, often comparing internal combustion devices, but the core of a turbofan engine is not an internal combustion device. Air/fuel mixture is just one of many purposes for core intake. Much less than half of this core airflow is mixed with fuel & then combusted; most airflow is used for cooling, with some used to separate the flame from the inside surface of the combustors, some directed outside of the combustors, some used to cool the interior of turbine blades, and some used to manipulate pressure gradients for sealing purposes.